1. Field of the Invention
The present invention relates to a mounting plate for a wire sawing device. It also relates to a wire sawing device comprising such a mounting plate, the device being designed to saw at least one piece to be sawed and comprising at least one layer of wires stretched out between at least two wire guide cylinders, said layer of wires being held in place by grooves provided on the surface of the wire guide cylinders, said wires being adapted to move in a reciprocating or continuous motion while bearing against at least one piece to be sawed that is fastened to at least one support table, while means of displacement are provided to accomplish a relative forward movement between the piece to be sawed and said layer of wires. The invention further relates to a wire sawing process carried out by such a wire sawing device.
2. Description of the Related Art
Wire sawing devices and processes of the type just cited that implement a displacement of the wires of the layer of wires or of the piece to be sawed are already known, especially in the industry of electronic components of ferrites, quartzes, and silicas, as well as in the Photovoltaic industry, for winning thin slices of materials such as polycrystalline or single-crystal silicon or of materials such as GaAs, InP, GGG, or again quartz, synthetic sapphire, and ceramic materials. In technologies, such as semi-conductor technology, the slices are called wafers.
In the known devices, the sawing section consists of a set of at least two cylinders placed in parallel. These cylinders, called wire guides, have grooves engraved into their surface that define the interval between the wires of the layer, and hence the thickness of the slices.
The piece to be sawed is named an ingot. It is fastened to a support table that moves perpendicularly to the layer of wires. The speed with which it moves defines the cutting speed. Renewal of the wire and control of its tension occur in a part called wire management section that is situated outside of the sawing section proper. The sawing is accomplished by means of an abrasive agent that is, either an abrasive fixed on the wire or a free abrasive brought in as a slurry. The wire merely acts as the transport agent. The pieces to be sawed, often come in the shape of a cylinder with quadrilateral, pseudo-quadrilateral, or circular base.
In known wire sawing devices such as illustrated in FIG. 13, the piece 110 to be sawed is fastened to the support table 120 in an indirect way. The piece 110 to be sawed is bonded to a temporary plate 112, usually known as a “beam”, that in turn is bonded to an assembly plate 114, usually known as a “gluing plate”. The assembly plate 114 in turn is fastened with assembly screws 116 to an ingot holder, e.g. a carriage 118 engaged in a guide rail of support table 120, and fastened to this support table 120.
Temporary plate 112 is a disposable part. It is made of glass or of a synthetic material, such as a thermoplastic material or a thermoset material or a composite material, into which the sawing wires penetrate after having cut through the piece 110 to be sawed.
Temporary plates made of glass offer a very good stability and eliminate the risk of warping of the slices obtained. Usually glass plates are produced at low cost. However, they become high cost products as soon as they need to be provided with cavities, such as holes and/or grooves and/or channels, because such cavities can only be obtained by machining the glass plates, which is an expensive process.
Temporary plates made of a synthetic material have the advantage that various designs of the plates can be achieved much easier due to the manufacturing option, but may have the disadvantage of undergoing warping deformation of the slices obtained. Also a plate made of a synthetic material such as a thermoplastic material or a thermoset material or a composite material shows a higher unit price than a glass plate.
Assembly plate 114 is made of a metallic material, for instance steel or aluminium. It is designed to be reused, so that after each sawing operation its surface must be cleaned, since the temporary plate 112 had been bonded to it during the previous operation. In the usual sawing process, the piece to be sawed is taken out of the wire sawing device when the sawing operation is finished. It appears as a set of parallel slices separated from each other by the saw nick or sawing gap, and at their base these slices are attached to a lug that is part of the temporary plate of glass or synthetic material into which the wires of the layer of wires have partially penetrated.
Because of the presence of the abrasive agent such as slurry, the slices tend to stick to each other due to a capillarity effect, this effect starting while the slicing process is still ongoing, but being emphasized once the slicing process is accomplished, the slices still hanging on the lug. Then the complete holding set, comprised of the ingot holder, the gluing plate, the beam and the piece sawed into slices attached to the lug, is taken off from the sawing device. This means, the slices are submitted to cleaning operations that occur outside the wire saw area. First, the slices still mounted on the holding set are immersed in a washing bath or in a rinsing bath, prior to a further washing or rinsing operation. The steps of washing, rinsing and separating the slices take place outside the sawing device.